There is currently much interest in overcoming the seasonality of sheep meat supplies in the UK and improving carcass quality. Towards that end, much research effort has been devoted to the development of techniques to induce early or out-of-season breeding in the ewe, but little attention has been paid to the male. Rams of most breeds show marked seasonal fluctuations In reproductive performance, with a depression in testis size, libido and semen quantity and quality during the spring and summer months and a period of high fertility in the autumn/winter, coinciding with the breeding season of ewes of the same breed. Problems of subfertllity which are frequently encountered following the use of various techniques to induce out-of-season breeding in the ewe may therefore be attributable, at least in part, to the ram. The choice of terminal sire for early lambing flocks is further compromised because some breeds of ram show later testicular recrudescence than others.